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QCX + Display troubleshooting

 

So far I have confirmed continuity between Microcontroller Pins 2,3,4,5, 6,27 to the LCD display pins.
Ground between Main board and display board is solid

I do get continuity on Pin 7 (VCC)? and Pin 20 AVCC of the microcontroller! not just Pin 8 and 22 which are ground BUT ONLY AFTER I PLUG THE DISPLAY BOARD INTO THE MAIN BOARD.
So I guess there is a short or something in the display board??

I suspect 2 x 3 mail header JP3 where I had actually solder this to the main board instead of the male header..and I did some work on that header to remove it and put it in right place.
The pins in the female look fine though and it passed the board to board continuity test...

So any thoughts appreciated.?
John-N2LK
 

John, it isn't clear to me. Sorry. Are you saying you are getting continuity from Vcc and AVcc to GROUND when you plug the two boards together? If so, then yes, you have a short on the display board somewhere. But that would cause some major smoke issues I would think, unless it has enough resistance to it to keep from loading down the 5v regulator.?

Anyway, if the above is not the case, please clarify?where you are seeing continuity that shouldn't be there. Thanks .. .Ron

On Fri, Oct 27, 2023 at 7:41?AM John Schreiner <jskcs1@...> wrote:
So far I have confirmed continuity between Microcontroller Pins 2,3,4,5, 6,27 to the LCD display pins.
Ground between Main board and display board is solid

I do get continuity on Pin 7 (VCC)? and Pin 20 AVCC of the microcontroller! not just Pin 8 and 22 which are ground BUT ONLY AFTER I PLUG THE DISPLAY BOARD INTO THE MAIN BOARD.
So I guess there is a short or something in the display board??

I suspect 2 x 3 mail header JP3 where I had actually solder this to the main board instead of the male header..and I did some work on that header to remove it and put it in right place.
The pins in the female look fine though and it passed the board to board continuity test...

So any thoughts appreciated.?
John-N2LK

 

What resistance are you calling continuity ?? ?(esp between VCC and AVCC !!!)
 

Hi Ron, I stand corrected. Now after some solder retouching here and there, VCC and AVCC are now not grounded...I even powered up the unit and measured around 4.84V I think on pin 7..so that is cleared up, whatever it was.

I think the key here is R47..I have been measuring Pin 3 of the LCD while fiddling with R47. I get a Voltage range from say 3.8V - 4.9.? so when turned fully counter clockwise I read 3.8V on pin 3 of the LCD ...manual says should be 0.

Now again I have seen the contrast work and text come up...I have seen the menu screen but then it all fades away....this also has happened with R47 mostly counter clockwise. The backlighting still works, its the contrast that crashes.

I also get a fair amount of display instability occasionally. I even watched it fade off to death altogether 30 minutes ago LOL The backlight faded out. Like a cap draining or something...
The unit is open on a desk, so the headers are taking all the load. That may be doing that..

Any guidance appreciated. I have to learn to love troubleshooting..
Thanks, 73
John-N2LK
 

John, if the contrast pot is fully counter clockwise and still see voltage on the wiper then the low side of that pot is not properly grounded. Ground connections are the hardest ones to get good connections with as they take more heat to make it right. So check that area next.?

73¡­¸é´Ç²Ô

On Fri, Oct 27, 2023 at 11:16 John Schreiner <jskcs1@...> wrote:
Hi Ron, I stand corrected. Now after some solder retouching here and there, VCC and AVCC are now not grounded...I even powered up the unit and measured around 4.84V I think on pin 7..so that is cleared up, whatever it was.

I think the key here is R47..I have been measuring Pin 3 of the LCD while fiddling with R47. I get a Voltage range from say 3.8V - 4.9.? so when turned fully counter clockwise I read 3.8V on pin 3 of the LCD ...manual says should be 0.

Now again I have seen the contrast work and text come up...I have seen the menu screen but then it all fades away....this also has happened with R47 mostly counter clockwise. The backlighting still works, its the contrast that crashes.

I also get a fair amount of display instability occasionally. I even watched it fade off to death altogether 30 minutes ago LOL The backlight faded out. Like a cap draining or something...
The unit is open on a desk, so the headers are taking all the load. That may be doing that..

Any guidance appreciated. I have to learn to love troubleshooting..
Thanks, 73
John-N2LK
 

I soldered R47 contacts and had good contact on the ground pin from R47 to the Voltage regulator heat sink ground connection on other board.

I measure the resistance range of this R47 at min - 73 ohms and at max turn clockwise -0 125 ohms..thats the range I see..I dont see it go to zero
I also notices the VR getting warm, so I attached the back enclosure with nut to help as a heat sink.

I measured all the microcontroller pin voltages. I also see the display only flickers now and then goes to black..no back light staying on like before.

And then I see my meter telling me its pull 0.47A at 13.24V...and the enclosure was getting warm too...so I pulled the plug for now.

So, what is your rate and address for an ER visit LOL!!??
Thanks
John-N2LK
 

Hi John. Sounds like it¡¯s giving you fits. I¡¯ll email you privately. 73¡­ Ron

On Fri, Oct 27, 2023 at 14:25 John Schreiner <jskcs1@...> wrote:
I soldered R47 contacts and had good contact on the ground pin from R47 to the Voltage regulator heat sink ground connection on other board.

I measure the resistance range of this R47 at min - 73 ohms and at max turn clockwise -0 125 ohms..thats the range I see..I dont see it go to zero
I also notices the VR getting warm, so I attached the back enclosure with nut to help as a heat sink.

I measured all the microcontroller pin voltages. I also see the display only flickers now and then goes to black..no back light staying on like before.

And then I see my meter telling me its pull 0.47A at 13.24V...and the enclosure was getting warm too...so I pulled the plug for now.

So, what is your rate and address for an ER visit LOL!!??
Thanks
John-N2LK

 

It's been a while since I had to TS my QCX+, but in rx mode you should be drawing about 25mA from the PS! If you are drawing 0.47 A you have a short some place.!? Pull out the display board and see if the short goes away. If the short is in the display board you are lucky as there aren,t ,many places on this board where you can find a short to gnd. I would start looking at all the VCC pins to the ICS and measure with an ohmmeter to ground at each of these points until I find the pin that has a short. I did this last year and when I finally got around to the very small SM IC, I found a short, which was a factory made solder bridge!? I fixed it! And this got me started with learning how to solder and desolder SM parts via a practice kit I found on Ebay.
maxcy/ wt1v

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